PSI - Issue 22

Yihua Dou et al. / Procedia Structural Integrity 22 (2019) 33–42 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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Fig. 6 grid diagram and stress cloud diagram of TG3 sample (main view and side view) Table 4 comparison of the stress concentration coefficient around perforated hole with the results of finite element analysis

Comparison between the measured results of axial stress concentration coefficient and finite element analysis results

Comparison between the measured results and the finite element analysis results

sample

measured

Ansys result

relative error

measured

Ansys result

relative error

TG1 TG2 TG3

1.33 1.18 1.27 1.26

1.28 1.33 1.39 1.33

3.7%

1.38

1.33 1.46 1.42 1.40

3.6%

12.7%

11.26

15.8%

9.4% 8.6%

1.33 1.32

6.7%

average 8.7% Table 4 shows the comparison between the measured stress concentration coefficient around perforated hole and the results of finite element analysis. It can be seen from the table that the relative error between the measured stress concentration coefficient and the results of finite element analysis is approximately 8.6% less than 10%, which meets the accuracy requirements of petroleum downhole engineering. 4. Fracture mechanics analysis of perforated casing It can be seen from Fig.5 that, under the action of load, the perforated casing fractured along the direction of the line between the nearest two holes in the axial direction during the experiment. Therefore, it can be concluded that in addition to the above-mentioned stress concentration, the fracture mechanical properties of the perforated casing should also be taken into account to analyze the strength and safety of the perforated casing. In solid mechanics, the theory of stress concentration and fracture mechanics is also called double criterion theory. According to the theory, when the stress reaches the smaller between allowable stress of the strength and stress intensity factor, the member will be destroyed. For perforated casing, the perforated hole can be regarded as a semi-elliptic crack on the surface.